Known high-voltage components, for example distribution transformers, can have nominal voltages in the range of 10 kV to 110 kV for a power rating of several 100 kVA to 10 MVA, for example, and more. Distribution transformers have a considerable weight of several tons, for example, and are not operated redundantly in many cases. Nevertheless, such distribution transformers are subjected to a test at specified intervals in order to determine the extent to which they satisfy the specifications imposed on grid operation, such as those conditions with respect to an expected failure probability. A routine part of such tests is also a partial discharge measurement.
The partial discharge measurement is one of the most important non-destructive methods for detecting insulation faults. The disruptive discharge of an insulation material is known to occur at an internal weak point which could have previously exhibited partial discharge activity. For this reason, the measurement of partial discharges can help to prevent cost-intensive damage. The partial discharge measurement is therefore used for quality tests and for diagnosis in the factory and during in-situ testing of cables, geographic information system (GIS), power transformers or measuring transducers.
In this case, the in-situ testing of distribution transformers is important because both transportation of the distribution transformer to a test laboratory is avoided and downtimes caused by the testing can be considerably reduced.
In addition to a suitable voltage source and the test object itself, the main components of an in-situ partial discharge measuring system are a coupling capacitance, a high-frequency current transformer (partial discharge sensors), a spectrum analyser for a digital pulse recording system, a digital pulse recording system and a storage oscilloscope.
Further principles of the in-situ partial discharge measurements are described, for example, in “Grundsteine der TE-Messung an Transformatoren: Vor-Ort Erfahrungen aus offline-Messungen” [Foundations of partial discharge measurement on transformers: In-situ experience from offline measurements], Martin Hässig, FKH Jitka Fuhr, ABB Thomas Aschwanden, BKW FMB Energie AG.
The disadvantage of an in-situ partial discharge measurement proves to be the fact that the degree of difficulty in interpreting the results of a partial discharge measurement depends on the manifestation, e.g., the behavior of the partial discharge activity in the time and frequency domains, the partial discharge pattern and the temporal stability.